census_tract

Census tracts are identified by an up to four digit integer number and may have an optional two-digit suffix. The census tract codes consist of six digits with an implied decimal between the fourth and fifth digit corresponding to the basic census tract number but with leading zeroes and trailing zeroes for census tracts without a suffix.

For additional details refer to the Census Bureau website: https://www.census.gov/data/academy/data-gems/2018/tract.html